It is well-known that the partial pressure of oxygen in the atmosphere decreases with altitude. For this reason it is necessary to provide the pilot and crew of high altitude aircraft with breathing systems in order to prevent hypoxia at high altitudes. Some of such breathing systems involve the generation of oxygen onboard the aircraft. Such systems may, for example, utilize bleed air from the aircraft engine(s), wherein such bleed air is processed to produce a product gas of high oxygen content. At certain altitudes, or during certain maneuvers, or in the event of malfunction, the onboard generating system may not provide physiologically acceptable breathing gas. For this reason, most aircraft breathing systems utilizing onboard oxygen generating systems also utilize a stand-by supply of oxygen.
In breathing systems of the above-described type, breathing gas is provided to the pilot and crew members by breathing masks worn on their faces. The problem with this type of system is that a breathing mask typically prevents the wearer from breathing ambient or cabin air unless the mask is removed from the wearer's face. Thus, once the mask is in position on the face, the wearer must make use of the aircraft breathing system. In most cases, the onboard oxygen generating system does not become operative until the aircraft engines are turned on. Therefore, a pilot or crew member wearing a breathing mask in an aircraft cockpit before the engines are running typically must use the stand-by supply of oxygen. This results in an unnecessary depletion of the stand-by supply which also causes high logistic and maintenance requirements. To prevent stand-by supply depletion, the crew member may elect to let his mask hang and breathe ambient air. This is undesirable because it may result in a loss of communications. Breathing masks typically include an intercom system for pilot and crew communication. When the pilot or crew member lets the mask hang, the intercom usually must be turned off because of intercom noise pickup resulting from the hanging mask.
Many high altitude aircraft also have the capability of permitting pilot and crew ejection. An oxygen supply is required if it should become necessary to eject at a high altitude. Therefore, aircraft with ejection provisions also incorporate a bail out (or emergency) oxygen supply. In other words, the emergency oxygen supply ejects along with the crew. The emergency oxygen supply is usually in the form of an oxygen bottle mounted to the aircraft seat. In aircraft having either separate stand-by and emergency supplies, or combined stand-by/emergency supplies, depletion of the stand-by/emergency supply bottle during normal operations is not desirable from a logistics, maintenance, and operational usage standpoint.
The present invention provides an improved breathing system that addresses (a) the above-stated problem of inefficient utilization of stand-by oxygen, (b) provides a method of integrating the various supplies along with cabin air breathing provisions and (c) presents an automatic control method to minimize crew work load. Means to replenish stand-by oxygen to reduce logistics and maintenance are also disclosed. Prior art United States patents which are known to be pertinent to the present invention are as follows: Price, U.S. Pat. No. 2,582,848 issued on Jan. 15, 1952; Summers, U.S. Pat. No. 2,877,966 issued on Mar. 17, 1959; Turek, U.S. Pat. No. 3,215,057 issued on Nov. 2, 1965; Jackson, U.S. Pat. No. 3,410,191 issued on Nov. 12, 1968; Wachter, U.S. Pat. No. 3,425,333 issued on Feb. 4, 1969; O'Reilly et al, U.S. Pat. No. 3,500,827 issued on Mar. 17, 1970; Reiher, U.S. Pat. No. 3,593,735 issued on July 20, 1971; Cramer et al, U.S. Pat. No. 3,720,501 issued on Mar. 13, 1973; Vensel, U.S. Pat. No. 4,057,205 issued on Nov. 8, 1977; and Cronin et al, U.S. Pat. No. 4,419,926 issued on Dec. 13, 1983.